كيف يحسب الرقم الهيدروجيني pH للمحاليل؟ How to calculate pH and pOH?

يحسب الرقم الهيدروجيني بالعلاقة: pH = -log[H⁺]، وللمحاليل المائية عند 25°C: pH + pOH = 14. إذا كان pH 7 فالمحلول قاعدي. [الصيغة الرمزية الموزونة: pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴]

Theme A — Space, Time and Motion

A.2.12 Impulse and Momentum — IB Physics HL Revision Notes & Topical Questions

5 min read 10 parts Lesson 23 of 63 1 quiz

📚 IB Physics HL Hub / Topical Revision

Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution

pH = -log[H⁺]  |  pOH = -log[OH⁻]  |  pH + pOH = 14  |  [H⁺][OH⁻] = 10⁻¹⁴

Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14

Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.

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Lesson summary

A.2.12 Impulse and Momentum — IB PHYSICS SL notes: Define impulse, relate it to change in momentum and use force–time graphs to find impulse.Impulse = the product of the force applied and the time for which it acts, J = FΔt.J is in N s, F is the resultant external force in N and …

Short interactions
From the second law
Constant force
Equivalent effect
Linear rise and fall
Complicated pulse

Part 1 of 8Impulse

Impulse

Impulse the product of the force applied and the time for which it acts, J = FΔt.

J is in N s, F is the resultant external force in N and Δt the time in s.

Vector

Vector impulse is a vector in the direction of the resultant force.

Units

N s is the same as kg m s⁻¹, because 1 N = 1 kg m s⁻².

Short interactions

Short interactions kicking a ball, catching a ball and a collision are examples.

Measuring

Measuring the force and time are hard to measure directly, so impulse is found indirectly from momentum.

Part 2 of 8Impulse–momentum theorem

From the second law

F = Δp/Δt gives FΔt = Δp.

Statement

Statement the impulse of the resultant force equals the change in momentum, J = Δp = mv − mu.
m is the mass, v the final velocity and u the initial velocity.

Constant force

FΔt = Δp is used when the force F is constant.

Rebound

Rebound a ball arriving at +u and leaving at −v has Δp = −m(v + u), larger than simply stopping.

Equivalent effect

Equivalent effect a small force over a long time has the same effect as a large force over a short time.

Part 3 of 8Force–time graphs

Area

Area the area between the curve and the time axis is the impulse.

Constant force

Constant force the area is a rectangle, F × Δt.

Linear rise and fall

Linear rise and fall the area is a triangle, ½ × base × peak height.

Complicated pulse

Complicated pulse count squares or split into shapes.

Average force

Average force divide the impulse by the contact time; the peak force is greater than the average.

Change in velocity

Δv = area/m, so v = u + area/m.

Part 4 of 8Reducing and increasing forces

Reducing and increasing forces

For a given Δp

For a given Δp a longer contact time gives a smaller average force, F = Δp/Δt.
What the symbols mean: F = force (N) · Δt = time the force acts (s) · Δp = change in momentum (kg m s⁻¹); FΔt is the impulse (N s)

Crumple zones

Crumple zones they lengthen the collision time and reduce the force on passengers.

Airbags and seat belts

Airbags and seat belts they extend the stopping time.

Bent knees

Bent knees gymnasts and parachutists lengthen the landing time.

Cricket catch

Cricket catch the fielder draws the hands back to increase Δt and reduce the force on the hands.

Short contact wanted

Short contact wanted hammering a nail or hitting a golf ball needs a short contact and a high force.

Soft landing mats and helmets

Soft landing mats and helmets compressible materials increase the contact time.

Part 5 of 8Umbrella in rain and hail

Raindrops

Raindrops they splatter and roll off, with only a small change of momentum.

Hailstones

Hailstones they have larger mass and bounce back, so the change of momentum and the impulse are greater.

Result

Result more force is needed to hold an umbrella in hail than in rain.

Part 6 of 8Impulse with gravity and other forces

Resultant force

Resultant force the theorem applies to the resultant force.

Short contact

Short contact during a bounce the floor force is much larger than the weight, so the weight can be ignored.

Long duration

Long duration for a rocket engine, gravity must be included in the resultant.

Two colliding objects

Two colliding objects the impulses on them are equal and opposite, which proves conservation of momentum.

Part 7 of 8Estimating forces

Method

Method use F = Δp/Δt with a sensible contact time.

Header

Header a 0.43 kg ball changing momentum by about 6 kg m s⁻¹ in about 10 ms gives an average force near 600 N.

Car crash

Car crash a 70 kg passenger stopping from 14 m s⁻¹ in 0.10 s feels about 9800 N, over fourteen times the weight.

Crumple zone

Crumple zone doubling the time halves the force.

Curved force–time peak

Curved force–time peak count squares and convert the unit of one square.
- (force per square times time per square)

Part 8 of 8More from the specification

Key terms

Term	Meaning
Impulse	Product of force and the time it acts; equal to the change in momentum
Newton second (N s)	Unit of impulse and momentum, equal to kg m s⁻¹
Impulse–momentum theorem	The impulse of the resultant force equals the change in momentum
Average force	Impulse divided by the contact time
Force–time graph	Graph whose area gives the impulse
Contact time	Time over which a force acts during an interaction

Avoid these mistakes

Forgetting the sign change when a body rebounds — Δp = m(v − u) with v reversed.

Using the peak force as the average force — the average is impulse divided by time.

Confusing impulse with force — impulse is force multiplied by time.

Using the weight in a short collision — the contact force is far larger.

Taking the area under a force–time graph as velocity — it is momentum change.

Last updated: 15 October 2026